Present day communications technology is directed more and more to the use of optical fibers for transmission and hence the use of optical fiber cables containing a plurality of coated or sleeved optical fibers. The cables may take any of a number of forms such as a plurality of fibers contained within a tubular protective member, thereby forming a core or bundled together in protective loose tubes surrounding a central strength member. Alternatively, the fibers may be arrayed side by side on a ribbon member, with a plurality of such ribbons being stacked to form a high fiber count cable, and which are then enclosed in a protective plastic tube or jacket. Regardless of the type of cable used, splices are necessary for joining the ends of cables, and the fibers contained within them. It is necessary, therefore, to enclose the splices in a closure to contain and protect the splices of two or more fiber optic cables.
In metallic wire communications practices, a splice closure is used wherein the wire splices are stored and protected. Because of the innate strength of wire, it can be sharply bent to meet space limitations, and slack wire within the enclosure may be tightly coiled. Glass optical fibers, on the other hand, are of extremely small diameter and are relatively fragile, therefore, optical fibers must be treated more carefully in placing them, and their splices, within an enclosure. Thus, transmission capabilities may be impaired if the fiber is bent to less than an allowable bending radius to the point where the transmitted light is no longer completely contained within the fiber. In addition, the fibers are brittle and do not possess the strength and resistance to breakage that metallic wire does, hence, when bent too sharply, the fibers may break. The breakage problem is exacerbated by minute, even microscopic surface fractures which are vulnerable to stresses on the fiber. Thus, a protective sleeve over individual fibers or fiber bundles is often necessary to minimize surface damage to the fibers, especially in the region of the splice.
It is clear, therefore, that optical fiber cable is not amenable to splicing using techniques applicable to wire type splicing. The glass fibers cannot be twisted, tied, or tightly coiled in the same manner as individual wires, nor can they be crimped or tightly bent without breakage. These problems are especially acute with multifiber cables where individual fibers must be spliced in a manner which allows subsequent or future repair or rearrangement, and the need for providing ample fiber slack to obviate sharp bends at the splice, which place stringent demands on the splice closure.
Inasmuch as, at the splice point, the cable is opened up and the base fibers exposed, the only protection afforded the fibers is provided by the closure, which can provide only one or two layers of protection from the outside environment, the requirements therefor are more stringent than for the cable, which normally provides several layers of protection. The closure must anchor all cables stored therewithin, and it must be capable of withstanding torsional and axial loads transmitted by the cable to the closure so that the splices are protected from these loads. The closure must also seal the inner and outer sheaths of the cables and maintain the seal integrity under extreme environmental conditions. The sealing must also provide a moisture barrier sufficient to prevent any moisture from reaching the fiber optic splices.
Additional requirements for the closure are its ability to provide adequate fiber storage for slack fiber without damaging the fibers and without increasing signal attenuation; the ability to store any type of splice, such as, for example, discrete or mass mechanical, or discrete or mass fusion type splices while dampening and reducing vibration and other forces that tend to damage the splice or splices; and the ability to provide adequate grounding for the metallic strength members of the cables. The closure must also have the capacity to accept the highest fiber count cables available on the market.
One such closure, designated the AT&T UCBI closure, has been commercially available for a number of years. The closure itself is offered to customers as a basic shell without the components for anchoring and sealing the cables, for routing and positioning the fibers, for housing and protecting the splices, for grounding the metallic strength members of the cables, and for encapsulating the closure itself within a protective shell. For the closure assembly to meet the desired criteria set forth in the foregoing, the various components to be used with the closure must be ordered separately. Thus, each customer orders specific kits designed to accommodate the particular size cables, number of fibers, and splices to be used. As a consequence, there is an entire catalog of components of varying sizes and designs from which the customer makes the necessary selections. Increasingly there has been a demand that closures be supplied with the necessary components included in one package, thereby relieving the customer of the necessity of "customizing" his particular closure with the required components, and it has become a desideratum in the optical fiber splice closure art that the components necessary to complete the closure, such as the fiber splitter for routing fibers, the splice trays for holding the splices, a grip assembly for anchoring the cables entering and leaving the closure and for grounding the metallic strength members, and an overall protective cover for encapsulating the closure which can be quickly mounted or removed, be capable of universal application, thereby accommodating virtually any size of cable within a specified range of cable sizes and any type of splice.